There is a growing need to protect high value assets (HVAs) from approach by underwater swimmers. High value assets include, for example, ships, oil well platforms, and other facilities that can be approached by water.
Two issues generate the growing need. First, there is a fear that an underwater swimmer can damage or cause the HVA to malfunction via an explosive or other device. For example, a terrorist swimmer having a desire to do damage could place underwater explosives on the hull of a ship. Second, some military platforms are subject to underwater espionage. For example, a submarine has classified shapes and characteristics, for example, propeller shapes and characteristics, which can be observed by an underwater swimmer while the submarine is docked.
Active and passive sonar systems are known that can detect and classify underwater objects including underwater swimmers. However, mere detection and classification of an underwater swimmer does not prevent the underwater swimmer from approaching the HVA.
As is known, high peak pressure low frequency underwater sound can be uncomfortable, disorienting, incapacitating, or damaging to a swimmer, and in particular to an underwater swimmer, depending upon the frequency and the peak pressure of the underwater sound. The high peak pressure low frequency underwater sound not only can affect the hearing of an underwater swimmer, but can also affect the underwater swimmer's internal organs, causing pain, or even rupture.
As is also known, marine animals are also affected by loud underwater sounds. For example, active sonar systems used on some military ships are capable of producing low frequency sound of sufficient peak pressure to disorient or kill some marine mammals.